The 42 year-old Royal Marine NCO watched from prison by video link as his wife Claire and dozens of veterans packed the London courtroom.

He was convicted in November 2013 by a court martial in Bulford, Wiltshire.

During his trial Blackman said he believed the victim was already dead and he was taking out his anger on a corpse.

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The panel of five judges, headed by Lord Chief Justice Lord Thomas, heard at the time of the 2011 incident Blackman was serving with Plymouth-based 42 Commando in Helmand province in “ghastly” conditions which were a “breeding ground” for mental health problems.

Mr Goldberg told the court if the new psychiatric evidence had been before the court martial, “as it really should have been if the defence had been up to the mark”, then “they would have had to look at the evidence through fresh eyes, through different eyes, and in particular the evidence of Mr Blackman himself”.

Blackman shot the insurgent, who had been seriously injured in an attack by an Apache helicopter, in the chest at close range with a 9mm pistol before quoting a phrase from Shakespeare as the man convulsed and died in front of him.

Alexander Blackman in the footage taken from a colleagues headcam (Image: MOD)

He told him: “There you are. Shuffle off this mortal coil, you c***. It’s nothing you wouldn’t do to us.”

He then turned to his comrades and said: “Obviously this doesn’t go anywhere, fellas. I just broke the Geneva Convention.”

The shooting was captured on a camera mounted on the helmet of another Royal Marine.

He was “dismissed with disgrace” from the Royal Marines after serving with distinction for 15 years, including tours of Iraq, Afghanistan and Northern Ireland.

Blackman’s case has been referred to the court for review by the Criminal Cases Review Commission (CCRC), an independent body which investigates possible miscarriages of justice.